Help with SDHC Card Use

As a newbie to Linux, I have kept my AAO relatively stock, adding only Skype and Thunderbird and Lightning, and changing the Acer desktop menus around. I have an international trip starting next week, and will try to keep it simple until after then.

But I bought an 8gb SDHC card, and have been afraid to plug it in. Why? Because my understanding is that it will be 'merged' with the SSD and be under control of the OS. (Is this correct)? That is not what I want. I want to have only my own documents and files on there. For one thing, I may use the card other places. For another, I will someday want to either replace it or augment it with a larger capacity card as they become even less expensive.

Is there any way to assure that the card will be under user control? And is there any way to make it easily available to applications? I tend to work from the file manager in Windows -- find the file(s) I want and open them from there, then save and close them from the apps.

Thanks in advance for any help you can give.


Ken

 

Sure, just use the Right Side SD slot, not the left one. It's only the Left Side SD slot that "merges" the card with your SSD.

Cheers.

 

The `merging' could be quite useful for users who don't want to have to worry about where their files are. Built-in apps will automatically have their files spread between the internal disk and the card, and the user doesn't have to worry. This is entirely the wrong thing to do if you want to be able to swap the card in and out, or if you care exactly where the files end up. As rbil says, just use the other slot. The left slot is really for a card that will be inserted and left there indefinitely.

 

It doesn't actually merge the files what it does is add a symlink to the built-in 8Gb for everything you add to the new SDHC. But you can load the disk into another reader and everything you put on it is there also you can use the advance mode in the Linpus file browser window and you will be able to see the disk separately.

 

It's not just a case of creating symlinks. When you insert a new card in the storage expansion slot it will create new directories `Picture', `Music', etc, and then create one `virtual' overall disk that combines these directories with those in the built-in disk. This not done with symlinks, but with a unification filesystem. The consequence is that if you just write files in /mnt/home (`My Disk') then they are automatically distributed between the internal and external disks, in a way that is outside the user's control. As you say, you can override this behaviour by finding the individual disk mount points and putting files there, but if you use the default locations then the actual final location of the file is outside your control. In practice, the AA1 tends to fill the internal disk first, and then start on the card.

The merge process also writes a load of hidden files on the card. This is done by the POSIX overlay to simulate a real unix-like filesystem on the card, which is probably formatted for windows. These files don't take up a lot of room, but they are a bit of a nuisance.

I don't think the storage expansion slot is intended to be a general-purpose card reader. It was intended to be a permanent (or at least semi-permanent) disk space expander. The right-hand slot, happily, does not behave this way.

 

Thanks, everyone. For my purposes, I will just use the right side slot. For whatever reason I assumed it took only normal SD cards, not the SDHC variety. When 32gb or 64gb cards become inexpensive enough, then I will plug one in there and be done with it.

Ken

 

Thanks for the outline of the merge function - I'll be trying to change that to good old automount, because I want to leave the card in the left hand reader most of the time (swapping it periodically between my Mac and the AA1 for my Eclipse projects), but I hate how the right-hand card sticks out so much.

A shame Acer didn't recess the card readers enough to make both flush.

Tim

 

You could always use another distro. As far as I know, the Linpus Lite version that comes with the AA1 is the only distro to use the left-hand card slot as memory expansion.

 

Kevin,

With Puppy Linux, the user creates a large file within which a complete ext2 filesystem is created. The filesystem holding that large file can be an ext3 filesystem; it doesn't have to be a FAT filesystem of any sort. That ext2 filesystem within the large file is overlaid over the original, which is never modified. I believe Fedora must do something similar with their livecd-iso-to-disk utility which allows one to essentially boot the iso image off a USB stick and have some persistent storage on that stick. That being said, here's my question: When using memory expansion, does Linpus actually modify the original install, or are all modifications written to the SD card?

 

It appears to me that by going into Thunar and by setting view / side pane to "tree" the merger does not happen and you can treat the left SD/MMC slot as a normal slot. In fact, clicking on the card in Thunar gives the option to "unmount" as you would expect. I keep Thunar set up this way and no longer have the annoying problem of trying to figure out where the OS decided to put a particular file since, as far as I can tell, everything is saved to the internal SSD by default.

I routinely save and download to the 8GB SSD and frequently move files to the SD card for "permanent" storage. Seems I am always wanting to transfer files among the AAO, my Ubuntu laptop, my Nokia N800, etc., and "sneaker net" works great for this.

:geek:

 

So far as I can tell, with no a card in the slot you have a unification filesystem on /mnt/home with only one branch -- that branch is the `proper' home directory on /home/user. When you plug in the card you can an additional branch in the unification system, consisting of the directories in /media/disk. I am not certain whether a change is made to the system the first time you plug a card in -- I really can't remember because I plugged a card in moments after taking the unit out of the box.

I don't _think_ that the use of storage expansion modifies the internal disk in any significant way, and it doesn't break anything in the AA1 if you take the card out (apart from losing the data on the card, obviously).

Personally I think the whole storage expansion thing is needlessly complex. All Linpus really needed to do was to create a symlink in the user home directory to the card, and call it `My extra files' or something like that. It doesn't break anything if there's nothing on the end of a symlink, so cards could be inserted and removed OK. It would just require that the user know that `My extra files' only exists if a card is inserted. The Linpus storage expansion thing requires the overheads of a Posix overlay filesystem, just to allow Unix-like file permissions on a FAT32 card. But is this necessary in a single-user system, when the card will almost certainly just be used for document files and suchlike?

In any event, I've completely disabled it on my system, and I don't miss it. It's a very clever technological solution to a problem which never existed, in my view.

 

Thanks Kevin, I stand corrected. I quit using Linpus and was going by memory and forgot about the folders Linpus creates automatically. It is not a concern with Onelinux (Ubuntu for the AA1) as the 16Gb SCHC in the slot on the power cable side is formated as my home partition.

 

Hey folks, one last dumb question.

What happens if you put an SDHC cards that is partially populated? Will the OS write stuff on it? Will it clobber the files that are already there?

Thanks again,


Ken

 

Personally, I wouldn't do it. So far as I know, the AA1 won't delete anything, but the existing files may not be visible through the file manager unless you make a specific trip to the directory that maps to the card. And the AA1 _will_ create new directories and hidden files on the card. It's not just the way it was designed to work.

 

After reading around on here I was panicking about this.

I got an 8Gb Class 6 SHDC card today (£11.47 delivered from emaxusb on ebay), so tidied up my home stuff first (I wanted to remove everything already on SSD so my new home stuff would go into SDHC).

deleted everything i had in Pictures/Videos/Documents etc - they were copies anyway, so I can recopy easily.

emptied trash (in thunar file manager go->trash, file->empty trash)

OPTIONAL: I chose to tweak the auxfs settings to use SDHC first, if you don't do this then files will be saved on SSD/SDHC depending on which has more free space - which would also work fine. Command to change settings is:
$ sudo sed -e'63s:mfs:tdp:' -e'99s:appendrepend:' -i.1 /etc/aufs.act
(from http://macles.blogspot.com/2008/09/abou ... spire.html )

shutdown One.

Inserted new 8Gb SDHC card into left slot, booted up, after about 2 minutes I get a popup saying something like expanded filesystem now ready.

Thunar shows My Disk 13.9Gb

I've hooked up my external USB and copied back a bunch of pictures, documents, video's, all works like a charm.

So just wanted to post to anyone who just wants to plug in an SDHC card and boot up, it works like a dream ! If you did this on a brand new One, you don't have to do a thing first.